Exhaust gas recirculation (EGR) between an exhaust manifold and intake manifold may be regulated in many ways. One device for controlling EGR is presented in European Patent Application 0137282. This method describes controlling a series of valves in an attempt to achieve a desired EGR flow rate. In particular, valves are set to an open position in combinations that approach the desired EGR flow rate. In one example, the valves are selected from a binary pattern that represents a predetermined EGR flow rate. The selected binary pattern changes with engine speed and temperature.
The above-mentioned method can also have several disadvantages. Namely, the valves operate in a completely open-loop manner. That is, the engine controller selects a number and pattern of valves that are suppose to deliver the desired EGR flow rate. However, over time carbon deposits may alter the flow characteristics of the valves such that a different amount of EGR flows than is desired. In addition, since the valves are controlled in a binary fashion, the EGR flow rate will be interrupted and discontinuous when the number of open valves changes.
The inventors herein have recognized the above-mentioned disadvantages and have developed a system and method to deliver EGR to an internal combustion engine that offers substantial improvements.